I've actually been considering getting on of these for protection against hurricanes/tornadoes.

Article here.

-Blast

not a bad idea--make sure it's waterproof!!!!

There are some very good above ground storm/safe rooms available. I have noticed some differences in door design with some being very foolproof as to easy exit even with debris etc. A few have outward swinging doors which is scary. Some have paid good attention to ventilation.

Nothing inherently wrong with an outward opening door. They are far easier to secure because any impacts are absorbed by the frame and stops instead of just the bolts.

Any worries about getting trapped inside are handled by suitable design. Making the main doors sectional, like a dutch door, so debris that piles up leaves the top half free, is a simple adaptation.

Providing a secondary, or even a third, exit is easy and smart. Providing a removable section below ground, and an entrenching tool to make digging your way out less tiring, is a popular detail.

Storing tools to allow you to force your way out in good time is smart. A shovel, gloves and a pry bar is common sense no matter how the door is designed. A high-capacity hydraulic jack and suitable plates and blocking allowing you to force openings is an option. A standard 100 ton jack will lift off an M-1 tank, should you be unlucky enough to have one land on the door. The tools can be put to good use rebuilding and for rescue after you emerge.

There are certainly ways of making an in-swinging door strong enough but inevitably an in-swinging door uses valuable space.

One of the common flaws that inexperienced builders experience is that they fail to take flotation of the shelter into account. In the mid-60s there was a wave of bomb shelters that popped out of the ground of their own volition when an extended drought broke and the water table rose.

It is clear is that many were built but ten, twenty, fifty years later many of them are useless. The difference between those that stayed usable and those that didn't is that those that got used and visited often stayed in far better shape. The deciding factor in this was the style of entrance.

If you have to climb down a ladder the tendency is to avoid the space. The ones that stayed in good shape tend to have entrances that you can easily walk into. Ideally one you can walk into while carrying a box.

If you can conveniently walk in carrying something with both hands you can easily use the room for storage, a wine room, play room. Regular use means it will get cleaned and repainted. It means that emergency supplies are far more likely to be inventoried, rotated, kept in good condition.

We built a concrete safe room into our new house. It has 8" thick reinforced concrete (not block) walls.

Nice! Is this just a closet-sized safety room or did you reinforce one of the "normal" rooms? Is the concrete on the ceiling, too?

-Blast

These are very common in the midwest as tornado shelters. We have one in our basement. Typically, they are built under the front porch, so they have a concrete slab roof. Because of this, they are usually as big as the front porch is dimensionally.

Greg